Exploring the role of extracellular matrix components in TRP polycystin ciliary localization and function PKD2 encodes a transient receptor potential polycystin (TRPP) channel receptor protein found in non-motile, primary cilia of mammalian cells. In humans, PKD2 mutations result in Autosomal Dominant Polycystic Kidney Disease (ADPKD). In the nematode Caenorhabditis elegans, the polycystin-2 homolog, PKD-2, localizes to the primary cilia of male-specific sensory neurons (CEMs and RnBs in the head and tail respectively) where it is required for male mating behaviors. Given the ancient and evolutionarily conserved role for polycystin-2 in cilia, C. elegans will be used as a model to identify new genes required for ciliary receptor localization. Mutants were isolated from a forward genetic screen for PKD-2: GFP ciliary localization (Cil) defects. The cil-2(my2) mutants exhibit excess unusual PKD-2 accumulation at the ciliary base, cilium proper, and around the distal dendrite. Three-factor and deficiency mapping, whole genome sequencing, and single gene rescue experiments have determined that the cil-2(my2) allele is a mutation in the gene mec-5. MEC-5 is a unique collagen protein found in the extracellular matrix (ECM) surrounding touch receptor neurons. In touch receptor neurons (TRNs), MEC-1, MEC-5, and MEC-9 are found in the ECM, play a role in mechanosensation, and may localize degenerin/epithelial sodium channels (DEG/ENaCs) along the TRN. Preliminary data indicates that mec-1 and mec-9 regulate PKD-2::GFP localization in male-specific sensory neurons. Therefore current research will determine how these ECM proteins regulate localization and channel properties of the PKD-2 TRP polycystin channel. These studies will shed light on how sensory receptors like PKD-2 are targeted to cilia, and may advance the understanding and treatment of ADPKD.